|0 INTRODUCTION. . 14?. 



rately determined ideas with fixed expVessions. It is as 

 necessary in Natural History, as it is in Geometry ; and it 

 may be said to be in respect to the former, what the DefiV 

 nitions are in respect to the latter. In Natural History, 

 however, the Terminology has to surmount many more 

 difficulties than in Geometry, since it refers principally 

 to empiric notions. Hence, the more geometrical ideas can 

 be introduced into the mineralogical Terminology, the 

 greater advantage will be obtained ; because, by this means, 

 its explanations will approach the nearer to the character 

 of geometrical definitions. None of the other parts of 

 Natural History allow of the introduction of geometrical 

 ideas to so great an extent as the Natural History of the 

 Mineral Kingdom. 



. 14. THEORY OF THE SYSTEM. 



The Theory of the System determines the idea 

 of the Species in Natural History. It fixes the 

 principle of classification ; and upon the idea of 

 the species, it founds, according to this principle, 

 the ideas of the Genus, the Order, the Class, and 

 the Kingdom, in both the natural and the artificial 

 systems ,- the difference of these it likewise indi- 

 cates and explains. Lastly, by applying all these 

 ideas to Nature, the outline of the system thus con- 

 structed, is furnished with its contents, in confor- 

 mity to our knowledge of the productions of Nature, 

 as obtained from immediate observation. 



The Theory of the System contains the reasoning, or 

 philosophical part of the science, and consists in the pro. 

 *"" (duction of ideas of a greater extent, than those derived 

 immediately from observation. These are the ideas men- 

 tioned above. The fundamental proposition, in this part 

 pf the science, is the following: All things arc identical 



